Signal receiver for terrestrial and satellite broadcastings

Abstract

A signal receiver which is capable of receiving and demodulating a satellite broadcasting signal which is an FM signal and a terrestrial broadcasting signal which is an AM signal is disclosed. FM and AM signals are frequency-converted into signals having frequencies in a same intermediate frequency band by making common use of a radio frequency amplifier, a mixer, a local oscillator and an intermediate frequency filter. At the time of reception of an FM signal, the FM signal is demodulated in a phase-locked loop circuit, and a local oscillator is subjected to frequency modulation by a part of the demodulated signal, thereby constituting an FM negative feedback loop, and thus narrowing the occupied bandwidth of the FM signal. At the time of reception of an AM signal, the phase-locked loop circuit is used to regenerate a carrier, and the output signal of the phase-locked loop circuit is input to a multiplier to effect synchronous detection of the input signal. At this time, the FM negative feedback to the local oscillator is utilized to effect automatic frequency control, thereby achieving stabilization of the synchronous detection.

What is claimed is: 
     
       1. A signal receiver for selectively receiving a frequency-modulated signal and an amplitude-modulated signal, comprising: a radio frequency amplifying means for amplifying a radio frequency signal supplied from an input terminal;   a frequency converting means for frequency-converting the radio frequency signal into an intermediate frequency signal by mixing the radio frequency signal and an oscillation signal from a local oscillator in a mixer;   a signal selecting means for selecting a desired intermediate frequency signal from the signals having been subjected to the frequency conversion;   a channel selecting means for generating a signal required to select a desired receive signal;   a phase-locked loop means having a phase-locked loop circuit which operates in phase with a frequency of the intermediate frequency signal, an output of said phase-locked loop means being a demodulated frequency-modulated signal demodulated from said frequency-modulated signal when said input signal is said frequency-modulated signal;   a frequency feedback means for supplying the output of said phase-locked loop means so that an oscillation frequency of the local oscillator in said frequency converting means is changed in accordance with the output of said phase-locked loop means;   a control signal generating means for generating a control signal for changing respective working bandwidths of said phase-locked loop means, said signal selecting means and said frequency feedback means in response to the signal delivered from said channel selection means;   a tuning voltage generating means for generating and supplying a tuning voltage corresponding to the desired receive signal to the local oscillator in said frequency converting means in response to the signal delivered from said channel selection means;   a phase shifting means for π/2 phase-shifting the output of said phase-locked loop means;   a multiplying means for multiplying the output signal from said phase-locked loop means which has been π/2 phase-shifted in said phase shifting means and said intermediate frequency signal, an output of said multiplying means being a demodulated amplitude-modulated signal demodulated from said amplitude-modulated signal when said input signal is said amplitude-modulated signal;   a signal switch in means for selecting one of the outputs of said phase-locked loop means and said multiplying means to output said demodulated frequency-modulated signal when said input signal is said frequency-modulated signal and said demodulated amplitude-modulated signal when said input signal is said amplitude-modulated signal; and   a signal processing means for processing an output of said signal switching means to a signal which is able to be displayed.   
     
     
       2. A signal receiver according to claim 1, wherein said signal selecting means is a frequency-fixed filter. 
     
     
       3. A signal receiver according to claim 1, wherein said signal selecting means is a frequency-variable filter the frequency of which is variable in accordance with a control signal from said control signal generating means. 
     
     
       4. A signal receiver according to claim 3, wherein said signal selecting means is arranged such that the pass bandwidth thereof is changeable in accordance with a control signal from said control signal generating means. 
     
     
       5. A signal receiver according to claim 3, wherein said signal selecting means is arranged to perform frequency tracking in accordance with a demodulated signal output from said phase-locked loop means. 
     
     
       6. A signal receiver according to claim 2, wherein said signal selecting means has Nyquist characteristic by which a carrier corresponding to reception of an AM signal is suppressed. 
     
     
       7. A signal receiver according to claim 5, wherein said signal selecting mean employs the same pass bandwidth irrespective of whether the signal which is to be received is an FM or AM signal. 
     
     
       8. A signal receiver according to claim 4, wherein said signal selecting means changes the pass bandwidth in accordance with a control signal from said control signal generating means which control signal is representative of whether the signal which is to be received is an FM or AM signal. 
     
     
       9. A signal receiver according to claim 4, wherein said signal selecting means is arranged such that a signal is passed through a low-pass filter, amplified in a broad-band amplifier and then passed through a high-pass filter, the respective cut-off frequencies of the low and high-pass filters being changed in accordance with a control signal from said control signal generating means, thereby changing the pass bandwidth. 
     
     
       10. A signal receiver according to claim 1, wherein the loop bandwidth of said phase-locked loop circuit is changed in accordance with a control signal from said control signal generating means so that the bandwidth employed at the time of reception of an AM signal is narrower than that employed at the time of reception of an FM signal. 
     
     
       11. A signal receiver according to claim 1, wherein the loop bandwidth of an FM negative feedback loop is changed in accordance with a control signal from said control signal generating means so that the bandwidth employed at the time of reception of an AM signal is narrower than that employed at the time of reception of an FM signal. 
     
     
       12. A signal receiver according to claim 10, wherein said phase-locked loop means operates such that an output signal from a phase comparator which detects a phase difference between an oscillation signal from a voltage-controlled oscillator and an input signal is fed back to said voltage-controlled oscillator through a loop filter which effects band limitation so as to minimize the output signal from said phase comparator, said loop filter being composed of a filter section in which the output signal from said phase comparator is input to one end of a first resistor and a second resistor and a variable-capacitance element are series-connected between the other end of the first resistor and a ground electrode, and a gain-controlled amplifier which amplifies a signal taken out from the other end of said frist resistor, the loop bandwidth being varied by simultaneously changing the capacitance of said variable-capacitance element and the gain of said amplifier. 
     
     
       13. A signal receiver according to claim 10, wherein said frequency feedback loop means includes a filter which comprises a filter section in which the output signal from said phase-locked loop means is input to one end of a first resistor, and a second resistor and a variable-capacitance element are series-connected between the input end and a ground electrode, said first resistor having a coil connected in parallel to it, and a gain-controlled amplifier which amplifies a signal taken out from the other end of said first resistor, the loop bandwidth being varied by simultaneously changing the capacitance of said variable-capacitance element and the gain of said amplifier. 
     
     
       14. A signal receiver according to claim 1, wherein said signal processing means comprises a low-frequency amplifier which amplifies a demodulated signal, an inverse characteristic filter which compensates the frequency characteristics of the amplified signal, and a picture and sound signal processing circuit which decodes the compensated signal into a signal which is able to be displayed, whereby the increase in amplitude of the low-frequency component of the demodulated signal at the time of reception of an AM singal having a vestigial side-band is suppressed by the inverse characteristic filter. 
     
     
       15. A signal receiver according to claim 14, wherein said inverse characteristic filter is arranged such that a signal from the low-frequency amplifier is input to one end of a series circuit formed from a first parallel resonance circuit composed of a frist resistor and a first capacitor and a second parallel resonance circuit composed of a second resistor and a second capacitor, and a third resistor is connected between the other end of said second parallel resonance circuit and a ground electrode, so that a signal is taken out from the node between the third resistor and said second parallel resonance circuit and supplied to said picture and sound signal processing circuit.